264 Williams — Contact-metamoi^phisin near PeekskiU, 



Owing to the small amount of material the alkalies were not 



determined : 



(I.) (II.) 



SiO n 32-73 8*2-21 



A1 2 3 46-58 48-87 



FeO 5-12 2*50 



CaO 11-04 10-02 



MgO 1-00 0*32 



Xa 2 1-91 



Li 2 0-32 



H 4-49 4-61 



100-96 100' 



Under (TI) is given for comparison an analysis of the mar- 

 garite from Chester, Mass., made by the late Professor Law- 

 rence Smith. * 



The occurrence of margarite as a contact-mineral in the 

 Cortlandt schist inclusions is interesting in connection with 

 the occurrence under the same circumstances of corundum, 

 with which margarite is always associated. 



The amount of margarite in the schist inclusions varies very 

 much in different specimens. In some cases it forms a large 

 proportion of the entire mass, while in others it is associated 

 with a greater or less amount of the other contact-minerals. 

 In this manner the inclusions classed in this group grade insen- 

 sibly into those of the other groups, although it is a notewor- 

 thy fact that the margarite was not observed in those particular 

 inclusions in which corundum crystals were most abundant, 

 The microscopic appearance of the margarite is shown in Plate 

 YI, figure 6. 



In many of its features the Cortlandt area is quite unique 

 and yet it finds many close analogies in certain regions which 

 have recently been made the subject of detailed petrographical 

 study in Europe. The region which seems most closely to re- 

 semble the Cortlandt area is that so admirably described by 

 Teller and von John, near "Klausen in the Tyrol, f Here 

 occurs a large eruptive mass exhibiting many facies and closely 

 resembling the Cortlandt eruptives save in the absence of horn- 

 blendic and peridotitic types. The authors distinguish : Xorite, 

 Quartz-norite, Xorite-porphyrite and Quartz-mica- diorite. In 

 many instances also a monoclinic pyroxene is associated with 

 the hypersthene and enstatite. The close resemblance of the 

 Klausen to the Cortlandt area is furthermore increased by the 

 contact-phenomena produced in the adjacent schists. These, 



* This Journal. II, xlii, 1886. Original Researches. 1884. p. 120. 



f Geologisch-petrooxaphische Beitrage zur Kenntniss der dioritischen Gesteine 

 von Klausen in Siidtirol. Jahrb. der k. k. geol. Reichsanstalt. xxxii, 1882, pp. 

 589-684. 



